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AR 15806 (Archival Research)

Sun Jul 14 19:19:17 GMT 2024

Principal Investigator: Zhijie Qu
PI Institution: University of Chicago
Investigators (xml)

Title: The Rotation, Accretion, and Mass of the Milky Way Warm Gas Disk and CGM
Cycle: 27

Abstract
Above the thin disk of cold gas and stars lies a warm ionized disk with scale height of a few kpc, along with a circumgalactic medium that may extend to the virial radius (~250 kpc). These components produce absorption lines toward hot stars and background AGNs. From the existing data of many sightlines, we show it is possible to determine the warm gas density distributions in the Milky Way disk and CGM (and the gas mass), as well as their kinematics: the rotation of the CGM (and separately of the disk component); and the accretion rate (or outflow) of the gas. In particular, the data provide the power to determine the steepness of the CGM radial distribution, leading to a major improvement in the MW CGM mass, which is currently uncertain by an order of magnitude. We will measure the rotation of the CGM to an accuracy of about 10 km/s, which is significantly better than the X-ray determination of the rotating hot halo, and is an important angular momentum constraint on the formation of the CGM. The infall rate can also be extracted, which we already detect (5 sigma) with just 8% of the sample. These goals will be achieved by using the Si IV and C IV absorption systems with S/N > 10, for which there are 240 separate sightlnes in the COS archive: 170 external sightlines (mostly AGN); and 70 sightlines toward Galactic stars. This project will provide an accurate velocity field and the best large-scale distribution of the warm gas in the MW, which is crucial for understanding Galactic feedback and accretion.